Devices and compositions containing boron and silicon for use in neutron capture therapy

ABSTRACT

The present invention relates to a boron containing therapeutic composition comprising: (i) a boron component formed at least partly from boron-10; and (ii) a silicon component. The composition is of value in the treatment of cancers by boron neutron capture therapy or in the treatment of arthritis by boron neutron capture synovectomy.

This invention relates to new pharmaceutical compositions and methodsfor treating cancer and other diseases. More specifically the inventionrelates to new pharmaceutical compositions comprising boron andelemental silicon, and to methods of treating cancer or rheumatoid ordegenerative joint diseases using pharmaceutical compositions comprisingboron and elemental silicon.

Cancer remains a significant cause of death, particularly for oldermembers of the population. For example, twenty thousand citizens of theUSA contract brain tumours each year, more than a quarter of these beingglioblastoma multiform brain tumours, a cancer that is usually fatalwithin six months of diagnosis.

There are a number of principal methods by which cancer can be treated.

Surgery is ideally a one-time procedure that may cure many types ofcancer, particularly in its early stages, or extend the life of apatient. Surgery inevitably involves hospitalisation of a patient.

Alternatively radiation therapy, which involves the use of high energyX-rays or electron beams to kill cancer cells, can be used to treatcancer. Radiation therapy can be very effective, particularly when thecancer is treated in its early stages and when it is located in a smallvolume of the patient's body. The high energy radiation can cause damageto healthy tissue. The absorption of a higher dose by the tumour,relative to normal tissue, may be achieved by precise geometric targetlocalization, judicious computer aided treatment planning and accuratebeam delivery systems.

A third type of treatment for some cancers is brachytherapy. This is aform of radiation therapy in which the radioactive source is implanteddirectly into the tumour. An advantage of this technique is that theradiation can be delivered to a confined volume, limiting the effect tothe surrounding healthy tissue.

A further potential way of minimising radiation damage to healthy tissueinvolves the use of boron-10. The technique is known as boron neutroncapture therapy (BNCT) and employs thermal and/or epithermal neutrons,which are directed to the region of the tumour. The boron-10, located atthe site of the tumour, then interacts with the neutrons to producehighly energetic and cytotoxic lithium-7 and helium-4. The boron-10 andrelatively low energy neutrons, each individually, have no significantcytotoxic effect.

The radiation products from BNCT have a short path length of about 12 to13 microns, which is comparable to a cellular dimensions, and it followsthat relatively high concentrations of boron are required in the tumourfor the therapy to be effective. It would also be advantageous if theatoms of boron-10 should be distributed though a substantial part of thetumour. However, provided the interaction of the boron and neutrons onlyoccurs at the site of the tumour, any collateral damage will berelatively minor.

For the BNCT to be effective, between 3 and 30 micrograms of boron-10per gram of tumour have to be delivered to the affected site. Theseconcentrations are many times those of conventional pharmaceuticals. Forexample in photodynamic therapy, another 2 step process of treatingtumours, the levels of photosensitising drug are typically 100 to 1000times lower then the levels of boron needed in BNCT. Systemic toxicityis thus a major issue for boronated agents. Such targeting may primarilybe accomplished by selectively concentrating boron containing drugs inthe tumour.

Research has been conducted into the treatment of primary high gradebrain tumours (glioblastoma multiforme) and melanoma. The vehicle usedin such treatments was initially boric acid or borax (sodiumtetraborate). Other boron agents that have been used for BNCT includesulfhydryl-containing polyhedral borane (BSH) and boronatedphenylalanine (BPA).

The results of all phase I (toxicity) and phase II (efficacy) studieshave not yet shown a significant advantage for BNCT that would justifyphase III trials. A major difficulty is the limited targeting andretention of boronated agents by tumour cells. If agents and techniquescould be developed that would allow ten times the concentration of boronin the tumour cells relative to that in normal tissue, BNCT could beused for a much broader range of cancers. Current techniques result intoo little boron being localised in the tumour, or too high aconcentration in the blood of the patient.

The following papers provide background information for the presentinventon: Med. Phys. 25 (11), November 1998, p 2220-2225; RadiationProtection Dosimetry Vol 101, Nos 1-4, pp 431-434 (2002); and RadiationResearch 151, 235-243 (1999). Each of these papers describes the use ofsilicon devices in microdosimetry.

It is an objective of this invention to address at least some of theabove mentioned problems.

According to one aspect, the invention provides a boron containingtherapeutic composition comprising:

-   -   (i) a boron component; and    -   (ii) a silicon component.

The silicon component may comprise one or more of: resorbable silicon,biocompatible silicon, bioactive silicon, porous silicon,polycrystalline silicon, amorphous silicon, and bulk crystallinesilicon.

The silicon component may comprise one or more of: microporous silicon,mesoporous silicon, and macroporous silicon.

For the purposes of this specification, microporous silicon containspores having a diameter less than 20 Å; mesoporous silicon containspores having a diameter in the range 20 Å to 500 Å; and macroporoussilicon contains pores having a diameter greater than 500 Å.

The silicon component may substantially consist of p-type silicon.

The boron component may comprise boron-11. Advantageously the boroncomponent comprises boron-10.

For the purposes of this specification bioactive silicon is silicon thatis capable, when implanted in a patient, of forming a bond with tissueof a patient; resorbable silicon is silicon that is capable, whenimplanted in a patient, of resorbing at the site of a tumour in apatient; and biocompatible silicon is silicon that is biocompatible forthe purposes of anti-cancer treatment or treatment of arthritis. Certainforms of porous and polycrystalline silicon have been found to bebioactive and/or resorbable, as disclosed in PCT/GB96/01863.

For the purposes of the specification a patient may be either a human oran animal.

The boron-10 may form part of a sample of elemental boron and/or mayform part of one or more boron compounds.

Boron-10 has an extremely high capture cross section for thermal orepithermal neutrons. A thermal neutron is defined as a neutron having anenergy between 1×10⁻⁶ eV and 1 eV and an epithermal neutron is definedas having an energy greater than 1 eV and less than or equal to 10 KeV.

Preferably at least 15% of the boron atoms present in the boroncomponent have a boron-10 nucleus. Naturally occurring boron is 18.7%boron-10 and 81.3% boron-11. More preferably at least 95% of the boronatoms present in the boron component have a boron-10 nucleus. Morepreferably substantially 100% of the boron atoms present in the boroncomponent have a boron-10 nucleus.

The use of a boron component in combination with a silicon component hasseveral advantages. The doping of silicon with boron is already a verywell established process for electronic applications of silicon. Siliconis a material that is resilient to the radiation products from BNCT, isreadily processed by semiconductor processing techniques, and certainforms of silicon have favourable biological properties.

The therapeutic composition may comprise at least one implant. Thetherapeutic composition may comprise at least one silicon implant. Theor at least one of the silicon implants may have a largest dimensionbetween 0.1 microns and 2 mm. The or at (east one of the siliconimplants may have a largest dimension between 0.5 micron and 1 mm. Theor at least one of the silicon implants may have a largest dimensionbetween 0.5 microns and 0.1 mm.

The or at least one of the implants may comprise one or more of thefollowing: a seed, a pellet, a bead. The or at least one of the implantsmay comprise one or more of the following: a staple, a suture, a pin, aplate, a screw, a coil, thread, a nail, and a barb.

The therapeutic composition may comprise a multiplicity of implants.Each implant may comprise part of the silicon component and part of theboron component.

The or at least one of the implants may comprise resorbable silicon. Theor at least one of the implants may comprise resorbable porous silicon.

The therapeutic composition may form at least part of a single implant.

The therapeutic composition may comprise at least one microparticle. Thetherapeutic composition may comprise a multiplicity of microparticles.Each microparticle may comprise part of the boron component and part ofthe silicon component.

Preferably the largest dimension of the or at least one of themicroparticles is in the range 0.05 to 5 μm. More preferably the largestdimension of the or at least one of the microparticles is in the range0.1 to 3 μm. Yet more preferably the largest dimension of the or atleast one of the microparticles is in the range 0.15 to 2 μm.

The therapeutic composition may comprise a suspension, suitable forinjection into a patient, the suspension comprising a multiplicity ofmicroparticles, each microparticle comprising part of the boroncomponent and part of the silicon component. The suspension may comprisean isotonic solution.

A further advantage of the use of silicon is the availability ofsemiconductor techniques to fabricate small silicon structures, such asmicroparticles, microneedles, and/or microbarbs, which are well adaptedfor treatment of the type of cancer in question.

The boron component may be selected from one or more of the following:elemental boron, borax, boric acid, sulfhydryl-containing polyhedralborane (BSH) and boronated phenylalanine (BPA), silicon hexaboride(SiB₆), boron rich porphyrin conjugates, carborane cholesterolanalogues, borane salts, nucleosides containing boron clusters,oligonucleotides containing boron clusters, boron anti-body conjugates,boron containing thiouracil derivatives, boronated purine bases,K₂B₁₂H₁₂ and boronated pyridine bases.

The boron may be elemental boron residing as a substitutional impurityin the tetrahedrally coordinated lattice of crystalline silicon. Theboron may be elemental boron residing in the grain boundaries ofpolycrystalline silicon. The silicon component may comprise poroussilicon and the boron component may comprise elemental boron that islocated in at least some of the pores of the porous silicon or a boroncompound that is located in at least some of the pores of the poroussilicon.

Preferably the or at least one of the implants comprises silicon and hasa shape and composition such that the or at least one of the implants issuitable for brachytherapy.

Preferably the silicon component comprises resorbable silicon. Morepreferably the silicon component comprises resorbable silicon and theboron component is distributed through at least part of the resorbablesilicon.

The use of resorbable silicon in combination with a boron component isvery advantageous. This is because the resorption of the silicon whenplaced at the site of the tumour allows the boron component to bereleased in a form, such as boric acid, which allows the disseminationof the boron through the cancer cells.

If the boron is located in porous silicon, the release rate of the boronmay be tuned by altering the porosity and/or pore size of the poroussilicon. In general high porosities and high pore sizes have a higherresorption rate than lower pore sizes and low porosities. By tuning therelease rate of the boron component, the concentration of boron in thetumour may be maximised relative to the surrounding healthy tumour atthe time of neutron irradiation. A further advantage is that the poorsolubility of molecular BNCT agents such as BPA may be enhanced byincorporation in porous silicon.

If the boron is in the form of atoms located in the interstices betweenthe silicon atoms of the silicon component, for example as a result ofdoping the silicon by conventional techniques, then the resorption ofthe silicon may result in release of the boron in the form of relativelysmall molecules such as boric acid molecules, thus aiding dispersioninto the tumour cells. Further the interaction of the neutrons with theboron and with the surrounding tissue causes some localised heating andthis may assist the dissolution of the resorbable silicon.

The silicon component may be micromachined to fabricate one or moreimplants having a predetermined size and shape, the size and/or shapebeing chosen to minimise trauma and/or swelling and/or movement of theimplant.

The resorbable silicon may comprise derivatised resorbable silicon. Theporous silicon may comprise derivatised porous silicon, including thetypes of derivatised porous silicon disclosed in PCT/US99/01428 thecontents of which are herein incorporated by reference. Derivatisationmay be used to provide targeting of tumour cells. A ligand for cellmembrane receptors over-expressed in malignant cells may be covalentlylinked to the resorbable silicon sub-micron particles.

For the purposes of this specification derivatised porous silicon isdefined as porous silicon having a monomolecular, or monatomic layerthat is chemically bonded to at least part of the surface, including thesurface that defines the pores, of the porous silicon. The chemicalbonding, between the layer and the silicon, may comprise a Si—C and/orSi—O—C bonding.

Advantageously the therapeutic composition comprises between 0.01 and100 moles of boron per mole of silicon present in the silicon component.More advantageously the therapeutic composition comprises between 0.1and 10 moles of boron per mole of silicon present in the siliconcomponent.

Advantageously the therapeutic composition comprises between 0.01 and100 moles of boron-10 per mole of silicon present in the siliconcomponent. More advantageously the therapeutic composition comprisesbetween 0.1 and 10 moles of boron-10 per mole of silicon present in thesilicon component.

The therapeutic composition may comprise greater than 1021 atoms ofboron-10 per cm³ of the composition. The therapeutic composition maycomprise between 5×10²⁰ and 1.3×10²³ atoms of boron-10 per cm³ of thecomposition. The therapeutic composition may comprise between 10²¹ and3×10²² atoms of boron-10 per cm³ of the composition. The therapeuticcomposition may comprise between 1021 and 1.3×10²² atoms of boron-10 percm³ of the composition.

The therapeutic composition may comprise between 1 and 25 atomic percentof boron-10. The therapeutic composition may comprise between 1 and 5atomic percent of boron-10.

The therapeutic composition may comprise a cytotoxic drug, and thecytotoxic drug may be selected from one or more of: an alkylating agentsuch as cyclophosphamide, a cytotoxic antibody such as doxorubicin, anantimetabolite such as fluorouracil, a vinca alkaloid such asvinblastine, a hormonal regulator such as GNRH, and a platinum compoundsuch as cis platin.

The therapeutic composition may comprise a water miscible organicsolvent. The therapeutic composition may comprise one or more of:methanol, ethanol, 1-propanol, 2-propanol, 1-propen-3-ol (allylalcohol), 2-methyl-2-propanol (tertiary butyl alcohol), diacotonealcohol, N,N,-dimethylformamide, dimethylsulfoxide, 1,3-dioxane,acetone, pyridine, tetrahydrofuran, ethylene glycol, and propyleneglycol.

Preferably the therapeutic composition comprises an ionic carbonate,more preferably the therapeutic composition comprises calcium carbonateand/or sodium carbonate.

Advantageously the therapeutic composition comprises a hydride, morepreferably the therapeutic composition comprises a hydride that may beoxidised by contact with a freshly prepared silicon surface.

The therapeutic composition may comprise a gas such as carbon dioxideand/or hydrogen.

Preferably the therapeutic composition comprises a foaming agent.

Carbonates may act as a source of carbon dioxide and hydrides may act asa source of hydrogen once they have been implanted. The release of gassuch as carbon dioxide and/or hydrogen may assist the dispersion of theboron component through the tumour. The dispersion of the boroncomponent may be further assisted by the use of a foaming agent whichmay interact with the gas to form a foam once the therapeuticcomposition has been implanted.

According to a further aspect the invention provides a therapeuticmethod, the method comprising the step of introducing a boron containingtherapeutic composition into a patient, the therapeutic compositioncomprising:

(i) a silicon component selected from one or more of: resorbablesilicon, biocompatible silicon, bioactive silicon, porous silicon,polycrystalline silicon, amorphous silicon, bulk crystalline silicon;and

(ii) a boron component formed at least partly from boron-10.

The silicon component may comprise one or more of: microporous silicon,mesoporous silicon, and macroporous silicon.

For the purposes of this specification, microporous silicon containspores having a diameter less than 20 Å; mesoporous silicon containspores having a diameter in the range 20 Å to 500 Å; and macroporoussilicon contains pores having a diameter greater than 500 Å.

The silicon component may substantially consist of p-type silicon.

The boron component may comprise boron-11. Advantageously the boroncomponent comprises boron-10.

The boron component may be selected from one or more of the following:elemental boron, borax, boric acid, sulfhydryl-containing polyhedralborane (BSH) and boronated phenylalanine (BPA), silicon hexaboride(SiB₆), boron rich porphyrin conjugates, carborane cholesterolanalogues, borane salts, nucleosides containing boron clusters,oligonucleotides containing boron clusters, boron anti-body conjugates,boron containing thiouracil derivatives, boronated purine bases,K₂B₁₂H₁₂ and boronated pyridine bases.

Preferably the method further comprises the step of irradiating thepatient with thermal and/or epithermal neutrons.

Advantageously the method comprises the step of irradiating the site orsites at which a cancer is located with thermal or epithermal neutrons.

The therapeutic method may be a method of boron neutron capture therapy.The therapeutic method may be a method of boron neutron capturesynovectomy.

The therapeutic method may be a method of boron neutron capture therapyand may be used for the treatment of micrometastases. The therapeuticmethod may be a method of boron neutron capture therapy and may be usedfor the treatment of micrometastases located in the lungs, bone, thebrain, the liver, colon, rectum, breast, ovaries, pancreas, stomach,uterus, testicles, and/or nerve tissues.

The therapeutic method may be used to treat malignant conditionsincluding the treatment of immune disorders and to treat rheumatoid ordegenerative joint dieases.

The therapeutic method may comprise the step of direct intratumouraldelivery of the therapeutic composition.

The therapeutic composition may be introduced to the tumour with greatprecision using a variety of techniques.

The therapeutic method may comprise the step of using one or more of thefollowing techniques: computer tomography, ultrasound, gamma cameraimaging, positron emission tomography, and magnetic resonance tumourimaging.

The boron-10 may be in the form of elemental boron or in the form of aboron compound.

Preferably at least 20% of the boron atoms present in the boroncomponent have a boron-10 nucleus. More preferably at least 95% of theboron atoms present in the boron component have a boron-10 nucleus. Yetmore preferably substantially 100% of the boron atoms present in theboron component have a boron-10 nucleus.

Advantageously the therapeutic composition comprises between 0.01 and100 moles of boron-10 per mole of silicon present in the siliconcomponent. More advantageously the therapeutic composition comprisesbetween 0.1 and 10 moles of boron-10 per mole of silicon present in thesilicon component.

The therapeutic composition may comprise greater than 10²¹ atoms ofboron-10 per cm³ of the composition. The therapeutic composition maycomprise between 5×10²⁰ and 1.3×10²³ atoms of boron-10 per cm³ of thecomposition. The therapeutic composition may comprise between 10²¹ and3×10²² atoms of boron-10 per cm³ of the composition. The therapeuticcomposition may comprise between 10²¹ and 1.3×10²² atoms of boron-10 percm³ of the composition.

The therapeutic composition may comprise between 1 and 25 atomic percentof boron-10. The therapeutic composition may comprise between 1 and 5atomic percent of boron-10.

Advantageously the therapeutic composition comprises at least oneimplant, the step of introducing the therapeutic composition comprisingthe step of implanting the or at least one of the implants into the bodyof a patient. More advantageously the step of implanting the or at leastone of the implants comprises the step of biolistically implanting theor at least one of the implants into the site of the tumour.

The step of introducing the therapeutic composition into the patient maycomprise the step of introducing the therapeutic composition into thepart or parts of a patient's body in which cancer is located.

The step of introducing the therapeutic composition into a patient maycomprise the step of introducing the therapeutic compositionsubcutaneously, intramuscularly, intravascularly, intraperitoneally,and/or epidermally.

The step of introducing the therapeutic composition into a patient maycomprise the step of introducing the therapeutic composition into thelungs, bone, the brain, the liver, the colon, the rectum, breasts,ovaries, the pancreas, stomach, the uterus, testicles, and/or nervetissues.

The step of introducing the therapeutic composition into a patient maycomprise the step of introducing the therapeutic composition into tissueconsisting of vasculature or a duct.

Preferably the therapeutic composition comprises a multiplicity ofmicroparticles, each microparticle comprising part of the boroncomponent and part of the silicon component. Advantageously thetherapeutic product comprises a multiplicity of uniform microparticleseach uniform microparticle having a largest dimension in the range 0.05to 5 μm. More preferably the largest dimension of each uniformmicroparticle is in the range 0.1 to 3 μm.

Yet more preferably the largest dimension of each uniform microparticleis in the range 0.15 to 2 μm.

The therapeutic composition may comprise at least one implant. Thetherapeutic composition may comprise at least one silicon implant. Theor at least one of the silicon implants may have a largest dimensionbetween 0.1 microns and 2 mm. The or at least one of the siliconimplants may have a largest dimension between 0.5 micron and 1 mm. Theor at least one of the silicon implants may have a largest dimensionbetween 0.5 microns and 0.1 mm.

The therapeutic composition may comprise a multiplicity of implants,each implant comprising part of the silicon component and part of theboron component.

The therapeutic composition may comprise a multiplicity of boron-siliconimplants, each implant comprising part of the silicon component and partof the boron component.

The method of treating a cancer may be a method of brachytherapy, theimplant being implanted into the tumour or into at least one of thetumours.

The step of introducing a therapeutic product into the patient maycomprise the step of introducing the therapeutic composition to the siteor sites at which the cancer is located.

The step of introducing a therapeutic product into the patient maycomprise the step of introducing the therapeutic composition into one ormore tumours.

Preferably the therapeutic composition comprises a multiplicity ofmicroparticles suspended in an isotonic solution, and the step ofintroducing the internal therapeutic composition comprises the step ofinjecting the suspension into an artery or vein connected to and/orlocated in organ(s) in which the cancer is located.

The mode of administration of the therapeutic composition will vary withthe benign or malignant disorder.

The silicon component may comprise resorbable silicon, and the methodmay further comprise the step of introducing the therapeutic compositionto the site of the tumour or tumours and allowing the resorbable siliconto resorb.

The silicon component may comprise resorbable silicon, and the methodmay further comprise the step of introducing the therapeutic compositionto the site of the tumour or tumours and causing the resorption of theresorbable silicon to increase by irradiating the site of the tumour ortumours with thermal or epithermal neutrons.

The boron component may be distributed through part of the resorbablesilicon, or the resorbable silicon may form a barrier between the boroncomponent and the site of the tomour or tumours. The arrangement of theresorbable silicon and the boron component may be such that corrosion ofthe resorbable silicon results in release of the boron component intothe tumour.

The therapeutic composition may comprise a solvent, the boron andsilicon components being dispersed through the solvent in the form of asuspension. The step of introducing the therapeutic composition into thepatient may comprise the step of injecting the suspension into thepatient using a needle. The needle may be a flexible skinny needle.

The therapeutic composition may comprise a water miscible organicsolvent. The therapeutic composition may comprise one or more of:methanol, ethanol, 1-propanol, 2-propanol, 1-propen-3-ol (allylalcohol), 2-methyl-2-propanol (tertiary butyl alcohol), diacotonealcohol, N,N,-dimethylformamide, dimethylsulfoxide, 1,3-dioxane,acetone, pyridine, tetrahydrofuran, ethylene glycol, and propyleneglycol.

Preferably the therapeutic composition comprises an ionic carbonate,more preferably the therapeutic composition comprises calcium carbonateand/or sodium carbonate.

Advantageously the therapeutic composition comprises a hydride, morepreferably the therapeutic composition comprises a hydride that may beoxidised by contact with a freshly prepared silicon surface.

The therapeutic composition may comprise a gas such as carbon dioxideand/or hydrogen.

Preferably the therapeutic composition comprises a foaming agent.

Carbonates may act as a source of carbon dioxide and hydrides may act asa source of hydrogen once they have been introduced into the patient.The release of gas such as carbon dioxide and/or hydrogen may assist thedispersion of the boron component through the tumour. The dispersion ofthe boron component may be further assisted by the use of a foamingagent which may interact with the gas to form a foam once thetherapeutic composition has been implanted.

The therapeutic method may comprise the step of causing a gas to bereleased, at the site at which the therapeutic composition has beenintroduced into the patient. The release of gas in this way may causethe therapeutic composition to be dispersed through the tumour.

The therapeutic method may comprise the step of introducing atherapeutic composition, comprising solid carbon dioxide, into apatient.

According to a further aspect the invention provides a therapeuticcomposition comprising boron-10 and solid carbon dioxide.

According to a further aspect, the invention provides an internaltherapeutic composition, as defined in any of the above aspects, for useas a medicament. According to a yet further aspect the inventionprovides a use of an therapeutic composition, as defined in any of theabove aspects, for the manufacture of a medicament for the treatment ofcancer by boron neutron capture therapy.

For the purposes of this specification the term “patient” is either ananimal patient or a human patient.

Methods of introducing boron into bulk crystalline silicon are wellknown. For example traditionally boron is diffused into silicon from gasphase sources such as BBr₃, BF₃, and B₂H₆. The first step in all theseprocesses is the formation of boron oxide on the surface of the bulkcrystalline silicon. After reduction of the oxide to elemental boron,the boron atoms diffuse into the bulk crystalline silicon. Temperaturesat which diffusion typically occurs are usually in the range 900 C to1400 C.

According to a further aspect the invention relates to a method offabricating boron treated porous silicon, the method comprising thestep: (i) incubating a sample of porous silicon in a solution of a boroncompound, at a temperature between 20 C and 90 C for a period between 5minutes and 200 minutes.

The boron compound may be boric acid. The boron compound may beboronated phenylalanine.

Preferably the boron compound solution comprises a solvent selectedfrom: one or more of: ethanol, methanol, and propanol. More preferablythe method comprises the further step (ii) of removing the solvent fromthe porous silicon after the incubation step is complete.

The method of fabricating boron treated porous silicon may furthercomprise the step of complexing the boron compound with a sugar. Themethod of fabricating boron treated porous silicon may further comprisethe step of complexing the boron compound with a sugar prior to step(i). The method of fabricating boron treated porous silicon may furthercomprise the step of complexing the boron compound with sucrose.

Advantageously the method of fabricating boron doped porous siliconcomprises the step, performed after step (ii), of heating the boroncontaining porous silicon resulting from step (i) to a temperature ofbetween 800 C and 1500 C for an interval between 5 minutes and 10 hours.

Bulk single crystalline boron doped silicon wafers, that have not beenporosified, are commercially available having boron concentrations ofless than 8.6×10¹⁹ boron atoms per gram of silicon.

According to a further aspect the invention provides boron treatedporous silicon having a boron concentration greater than 10²⁰ boronatoms per gram of silicon.

Preferably the boron concentration is greater than 5×10²⁰ boron atomsper gram of silicon. More preferably the boron concentration is between5×10²⁰ and 10²⁴ boron atoms per gram of silicon. Yet more preferably theboron concentration is between 10²¹ and 10²² boron atoms per gram ofsilicon.

Advantageously the porous silicon has a porosity between 10% and 90%.More advantageously the porous silicon has a porosity between 50% and80%.

Preferably the porous silicon has a pore size between 2 nm and 500 nm.More preferably the porous silicon has a pore size between 5 nm and 250nm.

According to a further aspect the invention provides a method of borontreated porous silicon comprising the step of (i) melting a boroncompound, and (ii) allowing the molten boron compound to pass into thepores of the porous silicon.

Advantageously the porous silicon has a porosity between 10% and 90%.More advantageously the porous silicon has a porosity between 50% and80%.

Preferably the porous silicon has a pore size between 2 nm and 500 nm.More preferably the porous silicon has a pore size between 5 nm and 250nm.

According to a further aspect, the invention provides a method offabricating a therapeutic composition, the method comprising the steps:(a) melting a sample of silicon and a sample of boron, and (b) combiningthe sample of silicon with the sample of boron so that a molten mixtureof boron and silicon is formed, and (c) cooling the molten mixture ofboron and silicon.

The step (b) may be performed before or after step (a). The method offabrication may comprise the further step (d), of atomising the moltenmixture of boron and silicon, and cooling the atomized particles to forma boron-silicon particulate product.

The method of fabrication may comprise the further step of stain etchingthe boron-silicon particulate product to form a porosified particulateproduct.

Embodiments of the invention will now be described by way of example,with reference to the accompanying drawings, in which:

FIG. 1 a shows an SEM image of a sample of porous silicon that has beentreated with boric acid;

FIGS. 1 a and 1 b show EDX spectra of the sample measured at the upperand lower portions of the sample porous shown in FIG. 1 a;

FIG. 2 shows a SIMS profile for the sample of treated porous siliconshown in FIG. 1;

FIG. 3 shows a SIMS profile for a sample of porous silicon that has beentreated with isotopically enriched boric acid;

FIG. 4 shows a SIMS profile for a sample of porous silicon that has beentreated with boronophenylalanine (BPA) and boric acid; and

FIG. 5 shows a SIMS profile for a sample of porous silicon that has beentreated with a BPA-sucrose complex.

The therapeutic compositions of the present invention may have a varietyof forms suitable for administration by subcutaneous, intramuscular,intravascular, intraperitoneal, or epidermal techniques.

The therapeutic product according to the invention may be spherical,lozenge shaped, rod shaped, in the form of a strip, or cylindrical.

The silicon component may form part of or at least part of: a powder, asuspension, a colloid, an aggregate, and/or a flocculate. Thetherapeutic composition may comprise an implant or a number of implants,the or each implant comprising the silicon component and the boroncomponent. Such an implant or implants may be implanted into an organ inwhich a tumour is located in such a manner as to optimise the effect ofthe anti-cancer component.

Treatment of a Tumour with a Suspension

The invention includes a suspension of microparticles, eachmicroparticle comprising a silicon component and a boron component foruse in BNCT of a target site in a subject. The microparticles aresuspended in an aqueous solution at a selected concentration. Theoptimal concentration will depend on the characteristics of themicroparticles, the type of therapeutic application, and the mode ofadministration. The aqueous solution may be one or more of water,saline, Ringer's solution, dextrose solution, and 5% human serumalbumin. The suspension may be isotonic with the patient's blood. Thesolution may comprise one or more buffers and/or one or morepreservatives and one or more excipients. The solution may comprisepolypeptides, proteins, amino acids, carbohydrates, or chelating agents.The suspension of microparticles may be administered via a very narrowdiameter needle, a catheter, or by the delivery channel of an endoscope.

Treatment of a Tumour with Brachytherapy

Physical accessibility of a tumour to be treated by brachytherapy isessential. Methodology for deep percutaneous access and intratumoralBNCT is similar to that developed for fine needle biopsy techniques.Examples of such techniques include: fine needle aspiration with 20-25gauge needle, and core needle biopsy in which 11-14 gauge needles areused. Single or multiple injections per tumour may be required. A reviewof relevant techniques and equipment for this form of administration isgiven in “Fine needle aspiration of soft tissue lesions” (Clin. Lab.Med. Vol 18, p 507-540 (1998)) which is herein incorporated byreference.

The present invention includes an implant, the implant comprising aboron component and a silicon component. The implant may be used fortreatment of a tumour with brachytherapy. The implant may beadministered using a needle or trocar (a sharp pointed instrumentequipped with a cannula). Placement of the implant can be guided byhigh-resolution ultrasound or computer tomography.

Ideally methods are used to intraoperatively visualize the needle ortrocar insertion into the site of the malignancy. This real-timevisualization affords enhanced accuracy of implant placement within thesite of the malignancy and allows for the identification and correctionof potential sources of error, such as movement of the malignancy andinternal tissue distortion that may occur during needle or trocarinsertion. This improved imaging ability and use of a needle or trocarobviates the need for surgical incision, permitting this procedure to bedone on a cost effective basis.

Alternatively, the organ to undergo the brachytherapy may be surgicallydebulked and the residual space filled with the therapeutic composition.In another aspect the organ to be treated may be cored with an array ofneedles and the cores back filled with the therapeutic composition.

Activation Within the Tumour

There is optimum time, after introduction of the boron-10, at whichneutron radiation is initiated. The calculation of the optimum time isdependent upon a number of factors. Effective BNCT is dependent upon asubstantial proportion of the administered boron-10 being retainedwithin the tumour prior to neutron radiation. Not only does the boron-10have to be at least partly retained in the tumour, but it should bedistributed through as much of the tumour as possible. The time takenfor these processed to occur may result in neutron irradiationcommencing between 30 minutes and 48 hours after the boron-10 has beenadministered.

Methods for delivering neutron beams of appropriate energy for use inBNCT are described in U.S. Pat. No. 4,516,535 which is hereinincorporated by reference. The patient may be positioned in front of thebeam of neutrons having energies between 0.5 and 30 KeV. The total dosedelivered to the patient may be less than 5×10¹² neutrons per cm².

Preparation of Boron Containing Therapeutic Compositions

Method A

Polycrystalline silicon beads, each bead having a diameter between 0.5mm and 2 mm and a purity of 99.99% are jet milled to yield reduced sizesilicon particles having a diameter between 2 and 6 microns. Thesereduced size particles are stain etched using HF/HNO₃ acid mixture toyield porous silicon particles. Boron doping to a level of higher than 1atomic percent may then achieved by incubating the powder in a boricacid/ethanol mixture at a temperature range of 30 to 80 C for between 5and 200 minutes. Optionally a further thermal drive in step may beemployed in which the porous particles are annealed at 600 to 1100 C for1 to 100 hours, followed by an HF dip.

Method B

A degenerately doped boron wafer is converted to an array ofmicroneedles by: standard wet etching techniques such as those describedin IEEE Transactions in Biomedical Engineering Vol 38, No 8, August1991, p 758 to 768.

Two sets of deep (200 micron) orthogonal cuts are made into a 380 micronthick wafer. The wafer is rotated by 90 degrees between the first set ofn cuts in one direction, and the second set of m cuts in the orthoganaldirection. This sawing does not cut through the wafer at any point butcreates an array of n×m square columns having an aspect ratio determinedby the spacing of the cuts. For a 75 micron wide blade and a pitch of175 microns one creates 100 micron wide square columns. The subsequentetching processes to define dart-like shapes then have 3 steps. Thefirst chemical etch is to remove saw damage, isotropically reduce thewidth of the columns and round the edges at the base of the columns. Itutilizes an HF: HNO3 etch (eg 5% to 95%) that is conducted with vigorousagitation. The second chemical etch is performed under static conditionsthat promote preferential attack of the top of the columns to createpointed tips and a tapered shaft. The third etch step is to create amechanical weakness at the base of the columns which facilitates theirdetachment from the underlying silicon membrane. This can be achieved bythe use of dry etch conditions that undercut the columns.

The narrow neck portions at the base of the needles may be formed bystandard deep dry etching techniques in combination with an etch stop(eg silicon oxide).

The needles may be porosified by standard stain etch techniques. Theboron concentration may then be increased by bringing the porosifiedneedles into contact with molten boron compound. The molten boroncompound is drawn into the pores of the porous silicon needles bysurface tension.

When implanted into the site of a tumour, the porous silicon microneedleor microneedles fabricated in this way can release boron both from theboron compound contained in the pores and from the interstitial boronlocated in the silicon itself.

Method C

A 0.005 to 0.015 Ωcm boron doped single crystal cz Si wafer is anodisedat 35 mA cm⁻² for 90 minutes in an electrolyte comprising equal volumesof 40% HF and ethanol. The applied current density is then raised to 117mA cm⁻² for 30 seconds. Upon subsequent rinsing in ethanol the entireporous silicon layer detaches from the underlying wafer as a membrane of65% porosity and thickness of approximately 150 microns. After airdrying, the membrane is first crushed manually in filter paper, and thenby pestle and mortar. After 1 hour of grinding in the pestle and mortarthe average particle size is reduced to less than 50 microns. An alkalibuffering agent such as anhydrous borax (Na₂B₄O₇) is then blended withthe porous silicon microparticles in dry form.

Method D

A p-type silicon wafer was anodised in 20% ethanoic HF solution at 32.5mAcm⁻² for 4 minutes. The silicon wafer was rendered p-type, prior toanodisation, by doping with natural boron, the resistivity of the p-typewafer being less 0.001 ohm cm. Natural boron comprises both boron-10(18.7%) and boron-11 (81.3%).

The anodisation generated a resorbable mesoprous layer of poroussilicon. Segments of the porosified wafer were then immersed in asolution comprising 2.5 g boric acid (H₃BO₃) in 25 ml ethanol (Aristargrade BDH) at 70 C for 15 minutes. The boric acid and ethanol solutionhas a pH of 4. This relatively low pH helps to prevent corrosion of theporous silicon. After removal, the segments were air dried at 100 Cwithout water rinsing.

FIG. 1 a shows an SEM image of the porous silicon, which has beentreated with boric acid; FIGS. 1 b and 1 c show EDX spectra of itscomposition at the upper and lower portions of the porous structure.FIG. 1 b corresponds to location 1 b in FIG. 1 a. FIG. 1 c correspondsto location 1 c in FIG. 1 a. The EDX spectra indicate that there is anincrease in the oxygen content of the porous silicon as a result of thetreatment with boric acid. The EDX results are consistent with aboronated oxide coating of the pore walls. The same sample of poroussilicon was subjected to Secondary Ion Mass Spectroscopy (SIMS) and theresults are shown in FIG. 2. The FIG. 2 SIMS plot shows the variation ofboron concentration with depth from the surface of the porosifiedsilicon wafer. At depths greater than approximately 3 microns from thesurface, corresponding to the bulk crystalline region of the wafer, theboron concentration is approximately 3×10²⁰ boron atoms cm⁻³. At lowerdepths, corresponding to the porous silicon region, the concentration ofboron atoms is in the region of 3×10²¹ boron atoms cm⁻³. Since naturalboric acid was used, the boron-10 concentration in the porous region is5.6×10²⁰ cm⁻³.

Method E

A p-type silicon wafer was anodised in 20% ethanoic HF solution at 70mAcm⁻² for 2 minutes, to yield resorbable mesoporous silicon. Thesilicon wafer was rendered p-type, prior to anodisation, by doping withnatural boron.

Segments of the wafer were then immersed in a solution comprising 0.7 gisotopically enriched boric acid in 12.5 ml ethanol (Aristar grade BDH)at 60 C for 5 minutes. The isotopically enriched boric acid comprisesboron atoms of which 99% are boron-10. The segments were air dried at100 C without water rinsing.

FIG. 3 shows the SIMS profile of the porosified wafer that has beentreated with isotopically enriched boric acid. The data reveals aboron-10 concentration of approximately 10²¹ atoms cm⁻³ throughout mostof the porous silicon region, which is more than a factor of 10 timeshigher than the boron-11 concentration. This boron-10 concentration, inthe porous silicon region, is equivalent to 2 atomic percent, or 1 boronatom per 50 silicon atoms.

As can be seen from FIG. 3, the concentration of boron-11 is relativelyconstant with depth. In other words, it does not vary significantly fromthe porous to the bulk crystalline region. This shows that the boron-11content of the porous region is due to natural boron present prior toanodisation.

The level of boron-10 in the porous silicon region, which has beentreated with isotopically enriched boric acid, is approximately 100times greater than the level that would have been present had the poroussilicon not been so treated.

Method F

Boronophenylalanine (BPA) is an FDA approved drug for BNCT. Itpreferentially accumulates in melanoma cells. Intravenous infusion ofBPA is a possible route for, targeted delivery to tumours, it has notbeen widely used due to the drug's poor solubility at physiological pH.

A segment of a porosified silicon wafer, prepared by the processdescribed in method D, was immersed in a suspension of BPA in a boricacid/ethanol/water solution. The boric acid was isotopically enriched(99% of the boron atoms being boron-10) and the BPA comprised naturalboron (81.3% of the boron atoms being boron-11). The composition of thesolution was: 0.7 g boric acid, 0.2 g BPA, 12.5 ml ethanol, and 12.5 mlwater. The low solubility of the BPA resulted in a supersaturatedsolution of the compound, having a milky appearance.

FIG. 4 shows a SIMS plot for the porosified segment that had beentreated with boric acid and BPA in the manner described above. Theboron-11 concentration in the porous region is not significantlyincreased relative to that of the bulk crystalline substrate. Thisindicates that very little drug has passed into the pores, despite clearinfiltration of the solution phase.

A solution of BPA and boric acid was prepared by a method described inU.S. Pat. No. 5,935,944 and U.S. Pat. No. 6,169,076 both of which areherein incorporated by reference; 0.2 g of BPA was added to 5 ml ofdeionised water, which results in a milky white suspension. 0.2 g ofsucrose and 9 ml of 0.2M NaOH were then added to increase the pH to 10,with the result that a clear solution is obtained. Within 2 minutes thepH is then reduced to 1 by the addition of 1 ml of 5M HCl. The solution,having a concentration of 13 mg/ml of BPA, remained transparent.

FIG. 5 shows an SIMS plot for the porosified segment that had beentreated with the BPA and sucrose solution prepared above. The prosifiedsegment was incubated in the solution 15 minutes at 50 C. The FIG. 5SIMS profile shows elevated levels of both carbon and boron within theporous region as a result of the BPA and sucrose incorporation.

Method G

A sample of metallurgical grade silicon may be placed in a vitreouscarbon crucible on top of a sample of isotopically enriched boric acidhaving a water content of less than or equal to 170 parts per million.The silicon and boric acid samples may then be melted by inductionheating, the temperature of the melt being in excess of 1420 C. In thisway a silicon alloy comprising between 0.1 and 1.3 atomic percent boronmay be fabricated. A similar process to this is described in U.S. Pat.No. 5,401,331, which is incorporated herein by reference. The moltensilicon alloy may be atomised and stain etched to yield solid poroussilicon particles comprising boron-10.

Method H

A film of silicon, comprising boron may be fabricated by vapourdeposition. For example silicon and boron hydride gases may bedecomposed to yield a silicon film comprising boron and hydrogen, aprocess that is described in U.S. Pat. No. 4,064,521, which isincorporated herein by reference. In a further example, boron mayincorporated in films of crystalline silicon in a non-equilibriumdeposition process such as that described in “Understanding ultrahighdoping: the case of boron in silicon” by Luo et al, Physical ReviewLetters Vol 90(2) p 026103-1 to 4 which is incorporated herein byreference. For example, gas source molecular beam epitaxy has achievedup to 25 atomic percent at 600 C on Si (001) substrates.

Once the film, comprising boron, has been deposited it may be renderedporous and resorbable by standard anodisation techniques. A porousmembrane may then be detached from the remainder of the film byincreasing the current density for an appropriate interval. The membranemay then be mechanically crushed and filtered to yield microparticlessuitable for administration to a patient via a fine gauge needle.

1. A therapeutic composition comprising: (i) a boron component formed atleast partly from boron-10; and (ii) a silicon component comprisingresorbable silicon.
 2. A therapeutic composition according to claim 1characterised in that the boron-10 is in the form of elemental boron. 3.A therapeutic composition according to claim 1 wherein at least 95% ofthe boron atoms present in the boron component have a boron-10 nucleus.4. A therapeutic composition according to claim 1 wherein the boroncomponent is selected from one or more of the following: elementalboron, borax, boric acid, sulfhydryl-containing polyhedral borane (BSH)and boronated phenylalanine (BPA), silicon hexaboride (SiB₆), boron richporphyrin conjugates, carborane cholesterol analogues, borane salts,nucleosides containing boron clusters, oligonucleotides containing boronclusters, boron anti-body conjugates, boron containing thiouracilderivatives, boronated purine bases, and boronated pyridine bases.
 5. Atherapeutic composition according to claim 1 wherein the boron componentcomprises boron atoms that are located in the interstices between thesilicon atoms of the silicon component.
 6. A therapeutic compositionaccording to claim 1 wherein the silicon component comprises poroussilicon.
 7. A therapeutic composition according to claim 6 wherein theboron component comprises elemental boron and/or a boron compound thatis located in at least some of the pores of the porous silicon.
 8. Amethod of treating a cancer, the method comprising: (a) introducing atherapeutic composition to a patient, the therapeutic compositioncomprising: (i) a silicon component comprising resorbable silicon; and(ii) a boron component comprising boron-10; and (b) irradiating thepatient with neutrons.
 9. A method according to claim 8 wherein theboron-10 is in the form of elemental boron or in the form of a boroncompound.
 10. A method according to claim 8 wherein at least 95% of theboron atoms present in the boron component have a boron-10 nucleus. 11.A method according to claim 8 wherein the method further comprises thestep of irradiating the patient with thermal and/or epithermal neutrons.12. A method according to claim 8 wherein the method further comprisesthe step of irradiating the site or sites at which the cancer is locatedwith thermal or epithermal neutrons.
 13. A method according to claim 8wherein the method comprises the step of introducing the therapeuticcomposition to the site of the tumour or tumours and allowing theresorbable silicon to resorb.
 14. A method according to claim 8, whereinthe method is a method of treating melanoma, the method comprising thestep of administering the therapeutic composition to the skin of apatient.
 15. A method according to claim 8, wherein the boron componentis present at a concentration of between 10²¹ and 10²⁵ boron atoms percm³ of therapeutic composition.
 16. A method according to claim 8wherein the internal therapeutic composition forms at least part of atleast one implant, the or at least one of the implants having a largestdimension between 0.1 and 100 microns.
 17. A method of treatingarthritis, the method comprising a steps (a) administering a therapeuticcomposition to a joint of a patient, the therapeutic compositioncomprising: (i) a silicon component comprising resorbable silicon; and(ii) a boron component comprising boron-10; and (b) irradiating thejoint with neutrons.
 18. A therapeutic composition according to claim 1,wherein the boron component is present at a concentration of between10²¹ and 3×10²² boron atoms per cm³ of therapeutic composition.
 19. Atherapeutic composition according to claim 18 wherein the internaltherapeutic composition forms at least part of at least one implant, theor at least one of the implants having a largest dimension between 0.1and 100 microns.
 20. A therapeutic composition, as defined in any one ofclaims 1 to 7 or claims 18 to 19, for use as a medicament.
 21. Atherapeutic composition, according to any one of claims 1 to 7 or claims18 to 19, for use in the treatment of cancer by boron neutron capturetherapy.
 22. A therapeutic composition, according to any one of claims 1to 7 or claims 18 to 19, for use in the treatment of arthritis.